As shown in Figure 2, despite large SDs there were marked and significant differences in the Ve/ VC02 ratio and the VE vs VC02 slope in patients with various NYHA and ability classes, while peak V02 did correlate to the symptomatic state to some extent.
The results of blood gas analysis are shown in Table 3. At rest, reduced Pa02 and increased VE (Table 2) were associated with slightly lowered PaC02 and HCO3 in cyanotic patients. During exercise, cyanosis worsened with a mean decrease in Pa02 of 25.8 ± 8% to 35.6 ± 9.8 mm Hg at end of exercise. In contrast, HCO3 was held within the normal range and PaC02 showed a nonsignificant increase with exercise.
Although mean pH at rest remained within the normal range, this parameter was closely correlated to VE/VC02 ratio (R2 = 0.56, p < 0.05), as well as to resting VE (R2 = 0.37, p < 0.05). However, this correlation was not apparent during exercise.
The resting Pa02 was correlated to the resting VE (Fig 3) and to Ve/Vco2 ratio (R2 = 0.26). A correlation between Pa02 and ventilatory efficiency (VE vs VC02 slope) was also found during exercise (R2 = 0.52).
Figure 4 shows the correlation of end-tidal partial pressures and VE vs VC02 slope. In eight patients, V02AT could not be determined by the V-slope method even after further inspection of V02, VC02,Ve/Vo2, and Peto2 kinetics. The exhaustion of breathing reserve at peak exercise, estimated by maximal VE/MVV ratio, was significantly lower in patients than in control subjects (0.43 ± 0.13 vs 0.58 ± 0.13, p < 0.05). this

Discussion Symptomatology and Exercise Gas Exchange
Patients with cyanotic congenital heart disease are generally thought to be limited by hypoxemia. Dyspnea, limited exercise capacity, lifestyle, and employment status are relevant factors for comprehensively evaluating the health of these patients. Consequently the ability index represents a supplemental tool in judging symptomatology. In this study, all patients stated an impaired quality of life. However, despite the severity of the cardiac malformations and the extent of cyanosis, 60% of the patients showed only moderate impairment of daily fitness.Figure 2. Mean CPX results for groups in different NYHA and ability classes compared to control subjects. Peak Vo2 is shown as milliliters of oxygen per kilogram per minute. *p < 0.05, compared to lower class; **p < 0.005, compared to lower class.
Figure 3. Ve at rest correlated to Pa02 at rest in cyanotic patients.
Figure 4. Correlation of exercise Peto2 (closed circles indicate control subjects; open circles indicate cyanotic patients) and exercise Petco2 (closed triangles indicate control subjects; open triangles indicate cyanotic patients) to Ve vs Vco2 slope.Table 3—Results of Blood Gas Analyses at Rest and Under Maximal Exercise